Sensor system for passive in-vehicle breath alcohol estimation

ABSTRACT

Methods and apparatus allow for passive determination of a driver&#39;s Breath Alcohol Concentration (BrAC). Alcohol concentrations can be determined from exhaled breath, however inconvenience to a driver is often a barrier for incorporation of BrAC sensors into vehicles. The methods and apparatus allow for passive determination of a driver&#39;s BrAC, while detecting and accounting for a wide range of environmental conditions that may reduce the accuracy of a passive BrAC reading.

CROSS REFERENCE TO RELATED APPLICATION

This claims the benefit of U.S. Provisional Patent Application No.62/312,476, filed on Mar. 24, 2016, the entire contents of which arehereby incorporated by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with Government support under contract numberDTNH22-08-H-0188 awarded by the Department of Transportation NationalHighway Traffic Safety Administration. The government has certain rightsin this invention.

FIELD OF THE INVENTION

This invention relates to methods for detection of breath alcoholconcentrations in the exhaled breath of a driver, and particularly forrapid estimations of a driver's breath alcohol level.

BACKGROUND OF THE INVENTION

Supervised breath tests are regularly performed by police in an effortto prevent drunk driving. In addition to supervised breath tests,automated ignition interlock devices, sometimes called “alcolocks,” thatconduct unsupervised tests to prevent the operation of vehicles by drunkdrivers, have been installed within vehicles themselves. Sensingtechnologies used for such breath tests may be based on catalytic beads(or pellistors), semiconductors, fuel cells or infrared spectroscopy.Typical breath test devices provide a signal representing Breath AlcoholConcentration (BrAC) after a driver has taken a deep breath and emptiedhis or her airways into a mouthpiece, which for hygienic reasons isoften a separate, disposable item. To ensure a correct determination,the test person is required to deliver a forced expiration at almostfull vital capacity. This requires substantial time and effort,especially for people with limited capacity. Ease of use, convenience,and accuracy are important factors for increasing the acceptance andadoption of built-in ignition interlock devices in vehicles.

SUMMARY OF THE INVENTION

There is therefore a need for a passive breath test that is flexibleenough to avoid inconvenience to the driver while ensuring accuracy ofthe test under a wide range of environmental conditions and driverbehaviors. In a passive breath test, the driver need not providedirected air to the sensor, and the BrAC measurement will be made,without additional action of the driver, from the air within thevehicle, which will be a mixture of breath of both the driver and anypassengers, as well as ambient air. In contrast, in an active breathtest, the driver may be required to be close to the sensor, and todirect a forced, undiluted breath towards the sensor or through an airinlet (e.g., blowing into a tube). While a passive breath test ispreferred, under some conditions it may not be possible to perform anaccurate passive breath test. Such conditions may be environmental(e.g., very hot weather) or the result of driver attempts to defeat thesystem (some examples are described below), but either way may result inthe air within the vehicle not accurately reflecting the driver's BrAC.If normal testing conditions, under which an accurate passive BrAC testis possible, are not met, then an active breath test is required.

A variety of parameters indicating both environmental conditions anddriver behavior are measured to detect when normal testing conditionsare no longer met. These include, for example, detecting a peak in atracer gas, which indicates that the driver's breath has been detected.A timer may set a time limit between when a driver's presence isdetected and when a peak in the tracer gas is detected. This time limitmay prevent driver attempts to defeat the system by holding his or herbreath, or otherwise concealing his or her breath from the sensor. Apressure sensor may detect situations in which a driver has attempted todefeat the system by ventilating the vehicle, or in which wind that isblowing through the vehicle may prevent an accurate passive breath test.Detecting the driver's head position relative to a sensor may ensurethat the driver's breath is being directed towards the sensor, in orderto prevent attempts to defeat the system by supply an alternate sourceof “breath” to be measured.

The methods and apparatus described herein allow for passive detectionof breath alcohol concentrations, and may be used for controllingignition of a vehicle. In particular, the methods and apparatus aredesigned to determine BrAC from a passive breath test withoutinconveniencing the driver during normal testing conditions, detect whennormal testing conditions no longer are met, and provide for BrACmeasurement from an active breath test under those circumstances.

In an example of a method or apparatus for passive breath alcoholdetection for operating a vehicle, the apparatus may include sensorswhich measure the concentration of a tracer gas in a passively obtainedfirst air sample, while the method may include initiating the sensorsystem, passively obtaining a first air sample, and measuring theconcentration from the first air sample. The apparatus may include aprocessor, which determines, using the sensor system, a set of testingconditions based in part on the first air sample, while the method mayinclude that determining. If the set of testing conditions is within anormal range and a peak in tracer gas concentration is detected, themethod or processor measures a BrAC of a driver from the first airsample. If the set of testing conditions is outside of the normal rangeor no peak in tracer gas concentration is detected, the method orprocessor requests an active second air sample from the driver andmeasures the BrAC of the driver.

In some embodiments, the method includes measuring a time intervalbetween initiating the sensor system and detecting the peak in tracergas concentration. In some embodiments, the apparatus includes a timerwhich measures that time interval. If the time interval exceeds apredetermined time limit, the method or processor determines that theset of testing conditions is outside of the normal range. In someembodiments, the apparatus includes sensors which measure theenvironmental conditions of the vehicle, and in some embodiments themethod includes measuring such environmental conditions. In someembodiments, such a sensor may be a temperature sensor, and in someembodiments the method includes measuring the temperature within thevehicle. If the temperature is outside a normal temperature range, themethod or processor determines that the set of testing conditions isoutside of the normal range. In some embodiments, the apparatus includesa pressure sensor to measure the pressure within the vehicle, and insome embodiments the method includes measuring that pressure. If thepressure is outside a normal pressure range, the method or processordetermines that the set of testing conditions is outside of the normalrange. In some embodiments, the apparatus includes a camera whichmeasures the driver's head position relative to a BrAC sensor, and insome embodiments the method includes measuring the driver's headposition relative to a BrAC sensor. In some embodiments, initiating thesensor system includes detecting the presence of the driver entering thevehicle. In some embodiments, measuring the BrAC of the driver from anactive breath test includes determining if a measured BrAC from apassive breath test is at an intermediate level. If the measured BrAC isat the intermediate level, the method requests an active breath sampleand measures BrAC. In some embodiments measuring the BrAC of the driverfrom an active breath test includes requesting, through a Human-MachineInterface (HMI), an undiluted breath sample directed towards the BrACsensor.

In some embodiments, the method includes sending sensor signals to acentral processing unit (CPU) of the breath test system, which is incommunication with a CPU of the vehicle. In some embodiments, theprocessor receives the sensor signals from the sensors. In someembodiments, the method includes disabling the operation of the vehicleif the result of the driver's BrAC measurement is above a set point,which may also be done with a processor. In some embodiments, the methodincludes enabling the operation of the vehicle if the result of thedriver's BrAC is below a set point, which may also be done with aprocessor. In some embodiments, the method includes requesting an activesecond air sample from the driver and measuring the BrAC of the driverif the result of a passive breath test of a first air sample is at anintermediate level. In some embodiments, the request may be made by aprocessor. In some embodiments, the method includes continuouslymeasuring air samples after initiating the sensor system, andcontinuously measuring the concentration of the tracer gas after thefirst air sample is measured. In some embodiments, the sensorscontinuously measure air samples after initiating the sensor system, andalso continuously measure the concentration of the tracer gas after thefirst air sample is measured.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features of the subject matter of this invention, its nature andvarious advantages, will be apparent upon consideration of the followingdetailed description, taken in conjunction with the accompanyingdrawings, in which like reference characters refer to like partsthroughout, and in which:

FIG. 1 depicts a flowchart of a process for determining a BrACmeasurement from passive or active breath samples, according to anillustrative implementation;

FIG. 2 depicts a flowchart of a process for determining the outcome of aBrAC measurement from a passive breath sample, according to anillustrative implementation;

FIG. 3 depicts a flowchart of a process for determining the outcome of aBrAC measurement from an active breath sample, according to anillustrative implementation;

FIG. 4 depicts a sensor for detecting breath and BrAC concentrationsfrom both active and passive breath samples, according to anillustrative implementation;

FIGS. 5A and 5B are an overhead view of a driver's head position inrelation to a sensor, according to an illustrative implementation; and

FIG. 6 is a graph representing examples of signals detected by aninitiation sensor and a BrAC sensor, according to an illustrativeimplementation.

DETAILED DESCRIPTION

Administering breath tests to drivers is an effective screening methodto reduce drunk driving and drunk driving related deaths. In breathtesting, a subject exhales air into a sensor or measuring device for asufficient time and of a sufficient volume to achieve breath flow thatoriginates from the alveoli of the lungs, where substances such as ethylalcohol (EtOH) in the blood are exchanged with air. The sensor ormeasuring device then measures the alcohol content in the air, which isrelated to blood alcohol through a conversion algorithm.

Existing breath based alcohol testing technologies require the driver todeliver a forced expiration at almost full vital capacity. This requiressubstantial time and effort, especially for people with limited lungcapacity. For hygienic reasons, the mouthpiece used in existing breathtesting devices may also need to be cleaned and replaced after multipleuses. Additionally, environmental conditions, such as wind, temperature,the presence of other people, etc. may significantly affect the accuracyof a BrAC measurement. To improve the adoption and public acceptance ofignition interlock devices in vehicles, a breath testing system thatdoes not inconvenience the driver and is robust under the wide range ofconditions found in a vehicle is needed.

There is therefore a need for a passive breath test that is flexibleenough to avoid inconveniencing the driver while ensuring accuracy ofthe test under a wide range of environmental conditions and driverbehaviors. In a passive breath test, the driver need not providedirected air to the sensor, and the BrAC measurement will be made,without additional action of the driver, from the air within thevehicle, which will be a mixture of breath of both the driver and anypassengers, as well as ambient air. In passive breath testing, the airwithin the vehicle is pulled into the sensor with a fan. The BrACmeasurement is made by first measuring the concentration of a tracergas, such as carbon dioxide, which indicates the dilution of thedriver's breath in the air within the vehicle. Then the measured EtOHconcentration can be combined with this breath dilution factor todetermine a BrAC. The BrAC measurement is thus made withoutinconvenience to the driver simply through sampling the air within thevehicle.

In contrast, in an active breath test, the driver may be required to beclose to the sensor, and to direct a forced, undiluted breath towardsthe sensor or through an air inlet (e.g., blowing through a tube). Inthe active breath test, BrAC is thus measured directly from the driver'sbreath, rather than through the air within the vehicle. The activebreath test requires action by the driver separate from the normalactions required to start the vehicle and may thus be considered moreinconvenient than the passive breath test.

While a passive breath test is preferred, under some conditions it maynot be possible to perform an accurate passive breath test. For example,the driver may attempt to defeat the system, resulting in the air withinthe vehicle not accurately reflecting the driver's BrAC. Similarly,environmental conditions within the vehicle (such as high wind from openwindows, or high temperatures after the vehicle has been standing closedin hot weather) may not allow for accurate BrAC measurement. If normaltesting conditions, under which an accurate passive BrAC test ispossible, are not met, then an active breath test will be required ofthe driver.

The present invention provides a variety of sensing checks to allow forpassive detection and estimation of a driver's BrAC under normalconditions, while switching to BrAC measurement from an active breathtest when normal conditions are no longer met. This reduces driverinconvenience by defaulting to a passive estimation of BrAC, whilesimultaneously providing alternative logic pathways when the accuracy ofa BrAC estimation is non-definitive, the driver behavior or testingconditions are outside of a norm.

FIG. 1 depicts a flowchart of a process for determining BrAC measurementfrom passive or active breath samples, according to an illustrativeimplementation. The process 100 starts at 102. Start 102 may beinitiated by a wireless door key to unlock the vehicle doors, by openingthe door to the driver's seat, or any other indicator capable ofsignaling that a driver has entered a vehicle. As the driver or testsubject takes the first steps towards entering the driver seat of thevehicle, process 100 will initiate sensors to monitor the testingconditions within the vehicle, the detection of a driver's breath, andto begin a timer to check whether a driver's breath has been detectedwithin a time limit during testing at 104. If a driver's breath isdetected (as determined at logic gate 106), the testing conditionswithin the vehicle are normal (as determined at logic gate 108), and thetime limit has not been exceeded (as determined at logic gate 110), thenthe process 100 will proceed to 112 and a BrAC measurement from apassive breath sample will be made. However, if either of the logicgates 106 or 108 make a negative determination, or a time limit has beenexceeded at 110, then process 100 will proceed to request from thedriver an active breath sample at 114.

The testing at 104 includes a self-test of all function blocks andsensors used in the process 100. At testing 104, stable operatingtemperatures of temperature-sensitive elements of any sensors used inprocess 100 are established. This may include, for example, the heatingof mirrors within a tracer gas detection sensor above 40° C. The mirrorsand tracer gas detection sensor are described in further detail withreference to FIG. 4. The self-test procedure conducted 104 may lastbetween 5-8 seconds in testing conditions at or above room temperature.The self-test procedure may last longer than 8 seconds at lowtemperatures. The testing at 104 may also entail measuring the initialconditions of the vehicle before the driver has entered, such as CO₂levels, EtOH concentrations in the vehicle air, air temperature, airpressure, etc. These initial conditions may be used to determine, atlogic gates 106 and 108, if driver breath has been detected and if thetesting conditions are within normal ranges, respectively.

A tracer gas may be any gas used to detect the driver's breath. Thetracer gas may be carbon dioxide (CO₂) or any other gas that mayindicate exhaled breath. The sensitivity of a tracer gas detectionsensor allows for detection of highly diluted exhaled breath, which mayhave a dilution factor (i.e. ratio between ambient air and undilutedbreath) greater than or equal to 50. Air is continuously drawn throughthe tracer gas detection sensor from the air within the vehiclefollowing initiation of the process 100. The tracer gas detection sensormay be located closer to the position of the driver's head than anypassenger position, e. g. at the steering column or side door nearestthe driver's side of a vehicle. Exhaled breath is recognized as a signalpeak output by the tracer gas detection sensor. If the tracer gas isCO₂, the baseline concentration of CO₂ corresponding to the baselinesignal is expected to be between 400 and 600 ppm (0.04%-0.06% volume).Tracer gas signals and initiation signals for 102 are described infurther detail with reference to FIG. 6. The tracer gas detectionsensor, which determines if breath is detected at logic gate 106, isdescribed in further detail with reference to FIG. 4. The breath samplein which the tracer gas detection peak is found may be the same breathsample used for the BrAC measurement at 112. Thus detecting a driver'sbreath during testing 104 and the logic gate 106 may occur approximatelysimultaneously to the BrAC measurement from a passive breath sample madeat 112.

Logic gate 108 may process the testing conditions of a vehicle anddetermine if they are within normal conditions capable of producing anaccurate BrAC measurement from a passive breath sample. Environmentalconditions may entail both the behavior of the driver and the state ofthe vehicle itself. These conditions may be detected by a variety ofsensors, including the tracer gas detection sensor, as well as auxiliarysensors placed throughout the vehicle. Sensors may include temperaturesensors to determine temperature within the vehicle, pressure sensors todetermine the barometric pressure within the vehicle as well as wind orair through the interior of the vehicle. Normal temperatures within avehicle may be within a range of −40° C. to 85° C. This may be thetemperature range over which a BrAC sensor can take accurate passivebreath tests. Normal barometric pressure may be within a range of 80 to105 kPa. This may be the pressure range over which mixing of thedriver's breath with ambient air can produce accurate passive breathtests. Temperature and pressure sensors may be any standard sensorelement and may be embedded in the body of the vehicle.

A camera sensor to monitor driver behavior may also be placed near thedriver, such as close to a steering wheel column. This camera sensor maydetect the position of a driver's head with respect to the tracer gasdetection sensor, as described in further detail with respect to FIG. 5.The relation between the driver's head and the tracer gas detectionsensor may determine if the driver is breathing in the direction of thetracer gas detection sensor. The camera may detect scenarios in whichthe driver is attempting to avoid detection of his or her BrAC by facingaway from the sensor. The camera sensor may also detect the presence ofunfamiliar objects near the driver's face, such as a mask, filter, spraybottle, or other object meant to interfere with the tracer gas detectionsensor, or to supply an alternate source of “breath” to prevent anaccurate passive breath test. The camera sensor may also detect theclose-by position of passengers, which may make it difficult todistinguish between the passenger's BrAC level and the driver's BrAClevel, or where the driver is attempting to have the system measure thepassenger's BrAC level rather than his or her own BrAC level. Logic gate108 may also determine the status of a vehicle's heating, ventilationand air conditioning (HVAC) system, such as whether it is in an ON stateor an OFF state. The HVAC system is preferably turned OFF or in a normaloperating condition during the process 100. Use of the HVAC systemduring passive breath testing may excessively dilute the driver's EtOHlevel, divert the driver's breath away from the sensor, or otherwiseprevent an accurate passive breath test. Logic gate 108 may also detectthe presence of windshield fluid. Windshield fluid typically includesethyl alcohol, which may influence the detection of EtOH within thevehicle. The windshield fluid is in an OFF state in normal testingconditions. Logic gate 108 may determine the states of both thevehicle's HVAC system and the state of the windshield fluid throughcommunication with the vehicle, such as with the vehicle's CPU orController Area Network (CAN) bus.

The logic gate at 110 determines if a time limit has been exceeded forprocess 100 to detect the breath of a driver during test 104. This maybe a predetermined time limit, such as from 10 to 30 seconds. If, at110, it is determined that this time limit has been exceeded, then theprocess 100 proceeds to a BrAC measurement from an active breath sampleat 114. The time limit may prevent situations in which a driver isavoiding breathing in the direction of the sensor, holding his or herbreath, has placed a mask over his or her head, or is otherwiseattempting to operate a vehicle without providing a breath sample. Inthis case, the logic gate at 110 will recognize that a breath has notbeen detected after the predetermined time limit, and will require anactive breath sample from the driver at 114.

If, at logic gate 106, the exhaled breath of a driver is detected, whilelogic gate 108 has determined that testing conditions are normal andlogic gate 110 has determined that a time limit has not been exceeded,then process 100 will proceed to a measure BrAC from a passive breathsample at 112. BrAC measurement 112 may be described in further detailwith reference to FIG. 2. If, however, breath is not detected at 106,then process 100 will continue to test for the breath of the driveruntil either a time limit is exceeded at 110 or unless normal testingconditions are not met at 108. In this case, process 100 will require anactive breath sample at 114 from which BrAC is measured. Thedetermination at 108 that normal testing conditions have not been met issufficient to require an active breath sample at 114. Similarly, if at110 it is determined that a time limit has been exceeded, process 100will proceed to an active breath sample at 114. The active breath sampleat 114 may be described in further detail with reference to FIG. 3. Theresults of BrAC measurements 112 and 114 may differ in accuracy.

FIG. 2 depicts a flowchart of a process for determining the outcome of aBrAC measurement from a passive breath sample, according to anillustrative implementation. Process 112 determines a driver's BrAC at202. Process 112 may be approximately simultaneous to the detection of atracer gas at 104 and 106, as shown in FIG. 1. Process 112 may thus becarried out using the same breath sample collected at 104 to detect apeak in tracer gas indicating the breath of a driver. The measurement ofBrAC is based on the dilution of a detected tracer gas, which may beCO₂. The detected dilution factor, or DF, of the tracer gas in thevehicle's ambient air is used to determine an estimate of the driver'sBrAC. The BrAC level may be determined according to the followingequation:

BrAC=EtOH*DF  (1)

DF is the dilution factor of the tracer gas in air. Additionalalgorithms may be used incorporating information from auxiliary sensors(not shown). The algorithm used measure BrAC from a passive breathsample at 112 may be different from the algorithm used to measure BrACfrom an active breath sample at 114. If the estimated value of BrAC isbelow a predetermined set point (denoted “Low” or “L”) then the process112 outputs a signal at 206 that the BrAC of a driver is “OK.” Thepredetermined set point may be in the interval of 0.1 to 0.4 mg/L (50 to200 ppm). The predetermined set point may be a function of the driver'sage. The predetermined set point may be a function of a legal limit onblood alcohol concentration for driving under the influence (DUI) ordriving while impaired (DWI). Signal 206 may be used to enable theoperation of a vehicle. If the estimated BrAC value is well above thepredetermined set point (denoted “High” or “H”), then the process 112will output a signal at 204 indicating that the BrAC of a driver is “NotOK.” A BrAC level of 0.1-0.2 mg/L (50 to 100 ppm) above said set pointmay cause the output of the signal at 204 indicating that the BrAC ofthe driver is “Not Ok.” Signal 204 may be used to disable the operationof a vehicle. If, at 202, it is determined that the BrAC of a driver iswithin an intermediate range (denoted “Intermediate” or “I”) slightlyabove or below the predetermined set-point, then further analysis of thedriver's breath is required to make a final determination. The driver isthen asked to perform an active breath test at 208. The active breathtest is described in further detail with reference to FIG. 3, and is theprocess 114 as shown in FIG. 1 and FIG. 3. A sensor, such as the sensordescribed in FIG. 4 may make the measurement at 202, while externalprocessing such as described in further detail in FIG. 4 may communicatethe signals 204 and 206 to a central processing unit, or CPU 415.

FIG. 3 depicts a flowchart of a process for determining the outcome ofan BrAC measurement from an active breath sample, according to anillustrative implementation. Process 114 begins at 302 where the BrAC ofa driver is measured. In the aBrAC measurement from an active breathsample at 302, a driver is requested to provide an active breath towardsa sensor (not shown) at a distance of 15-30 cm from the sensor. Thedistance may be adjusted for the location of the sensor within thevehicle. If the BrAC is below a predetermined set point (denoted “Low”or “L”) then the process 114 outputs a signal at 306 that the BrAC of adriver is “OK.” Signal 306 may be used to enable the operation of avehicle. If the estimated BrAC value is well above the predetermined setpoint (denoted “High” or “H”), then the process 114 will output a signalat 308 indicating that the BrAC of a driver is “Not OK.” Signal 308 maybe used to disable the operation of a vehicle. If, at 302, it isdetermined that the BrAC of a driver is within an intermediate range(denoted “Intermediate” or “I”) slightly above or below thepredetermined set-point, then the driver will be requested to provide abreath sample with evidential accuracy at 304. The breath test performedat 304 will require an undiluted breath sample. From test 304 there isno intermediate response. The breath test at 304 will require the driverto direct an active breath towards a sensor (not shown) at a distance of15-30 cm from the sensor. The distance may be adjusted for the locationof the sensor within the vehicle. If the measured BrAC value is below aset-point (L) then process 114 will produce an output signal at 306indicating that the BrAC of a driver is “OK.” If the measured BrAC valueis above a set-point (H) then the process 114 will produce an outputsignal at 308 indicating that the BrAC of a driver is “Not OK.”

The logic gates 106, 108, 110 in FIG. 1, 202 in FIG. 2, and 302 and 304in FIG. 3 are shown as representing “IF . . . THEN” logical statements,however these logic gates are not restricted to elements of Booleanlogic. Logic gates 106, 108, 110, 202, 302 and 304 may also demonstratefuzzy logic or be governed by artificial neural networks. The desiredlogic system may be programmed into a CPU 415 as described in furtherdetail with reference to FIG. 4.

FIG. 4 depicts a sensor for detecting breath and BrAC concentrationsfrom both active and passive breath samples, according to anillustrative implementation. The sensor 400 may detect breath duringtest 104 as shown in FIG. 1, measure initial conditions of the vehicleat 104, as well as perform both the BrAC measurement from a passivebreath sample 112 and the BrAC measurement from an active breath sample114 as shown in FIG. 1, and described in further detail with referenceto FIG. 2 and FIG. 3. The sensor 400 draws air continuously through aninlet 402, to an outlet 403, and measures for both the presence of atracer gas such as CO₂ and the presence of EtOH within the airflow. Thesensor 400 determines whether a driver's BrAC is within a Low, High orIntermediate range, as described with reference to FIG. 2 and FIG. 3.

The sensor 400 is contained within an enclosure 401, and may be astand-alone sensor or designed for integration into the interior of avehicle, such as within a steering wheel column, a side door, A- orB-vertical support pillars, a sun visor, dashboard, or other convenientposition significantly closer to a driver's head than to apassenger-designated area of the vehicle. The enclosure 401 may beairtight except for the openings at the sensor input 402 and outlet 403.The enclosure 401 may have the approximate dimensions of 25×40×120 mm.The air brought into the enclosure 401 through the inlet 402 is heatedto above body temperature by an inlet heater 404, which may avoidcondensation at low ambient temperatures. The inlet heater 404 may havea large surface contact area to the inlet air in order to improve heattransfer from the heater to the incoming air. The heater 404 may be aresistive heater. The air flow from the inlet 402 to the outlet 403 isdriven by a fan 411 located close to the outlet 403.

The sensor 400 measures the presence of both CO₂ and EtOH throughinfrared (IR) spectroscopy. IR spectroscopy uses the specific“fingerprint” that gas-phase alcohol produces when illuminated byinfrared light to determine an alcohol concentration within the airflowof the sensor 400. The detected absorption spectrum of any substance isa product of resonant molecular vibrations, which are specific to theatomic bonds within a molecule or compound in the breath sample. Fromthe absorption spectrum, particular substances and their absolute orrelative concentrations within the breath sample can be determined.

To perform IR spectroscopy and detect both the presence of a tracer gasand the presence of EtOH, the sensor air chamber tube 410 includes twoseparate optical paths, one for detection of a tracer gas and a secondfor detection of EtOH. The signals produced by these two optical pathsare used to determine the value of a dilution factor of the driver'sbreath in ambient air (or DF as shown in Equation 1) as well as thevalue of EtOH concentration within the input air.

The first optical pathway, composed of an EtOH IR emitter 406 and EtOHIR detector 407 as shown in FIG. 4 will determine an EtOH concentration.The EtOH IR emitter 406 outputs IR radiation into the interior of thesensor air chamber tube 410. A spherical mirror assembly composed of afirst mirror 405 placed at one end of the air chamber tube 410 and asecond mirror 412 located at the opposite end of the air chamber tube410 reflects the emitted IR radiation from the EtOH IR emitter 406. Theoptical path length of the emitted IR radiation may be several timesthat of the distance between the first mirror 405 and the second mirror412, as the mirror assembly will reflect the emitted light several timesbefore it hits the EtOH IR detector 407. The optical path is shown asdashed lines in FIG. 4, however this is shown as an example and theactual optical path between the EtOH IR emitter 406 and the EtOH IRdetector 407 may be much longer.

The EtOH IR emitter 406 may be a black-body radiator, IR laser diode, orany other optical source capable of producing IR light and preferablywith a small mass to fit within the air chamber tube 410. The EtOH IRemitter 406 may be modulated at a frequency between 5-10 Hz in order tosuppress low frequency noise and disturbances in the signal of the EtOHIR detector 407. The EtOH IR detector 407 includes a bandpass filterthat is tuned to the IR absorption peak for EtOH, which is approximately9.5 μm. The EtOH IR detector 407 may be a pyroelectric or photonicdetector, capable of producing a high resolution signal, and may alsoinclude a Peltier element for localized cooling in order to suppressthermal noise in the detection signal. The detection signal produced bythe EtOH IR detector 407 is described in further detail with referenceto FIG. 6. The sensor 400 is specifically designed for high resolutionIR spectroscopy measurements, and may have a resolution exceeding 0.5μg/L (or 1.2 ppm) of EtOH, enabling the estimation of alcoholconcentration in highly diluted breath.

The second optical pathway is dedicated to detecting the presence of atracer gas, such as CO₂, which will indicate the dilution of a driver'sbreath within the air input through the sensor 400. A tracer gas IRemitter 408 is placed opposite a tracer gas IR detector 409 such thatthe optical path from the tracer gas IR emitter 408 to the tracer gas IRdetector 409 is across the shorter dimension of the air chamber tube410. The tracer gas IR detector 409 may be tuned to a wavelength bandspecific to the IR absorption frequency of the detected tracer gas. Inan example where the tracer gas is CO₂, the absorption peak may be at4.26 μm. Due to the high end tidal concentration of CO₂ in exhaled air,which is typically at 4.2% volume, a short optical path across the airchamber tube 410 may be used. This path is indicated in FIG. 4 as adashed line between the tracer gas IR emitter 408 and the tracer gas IRdetector 409. The signal produced by the tracer gas IR detector isdescribed in further detail with reference to FIG. 6.

The signals from both EtOH IR detector 407 and tracer gas IR detector409 may be used to determine if normal conditions for the passivemeasurement of BrAC are met, such as during the test 104 and the logicgate 108 of process 100 as shown in FIG. 1. This may entail checkingthat the baseline presence of the tracer gas is within standard levels,such as the baseline concentration of CO₂ in ambient air.

The first mirror 405 and the second mirror 412 are both in communicationwith a central processing unit, or CPU 415 as shown in FIG. 4. The EtOHIR emitter 406, EtOH IR detector 407, tracer gas IR emitter 408 andtracer gas IR detector 409 may also be in signal communication with theCPU 415. CPU 415 processes the signal generated by the EtOH IR detector407 and the tracer gas IR detector 409 to determine BrAC measurements.

An HMI 413 is in communication with the CPU 415 and may be used tocommunicate with a driver to request an BrAC measurement from an activebreath sample. The HMI 413 includes audiovisual means for communicationwith a driver, such as a screen and speakers to convey messages and arequest for an active breath test, as well as other directions to adriver. The HMI may display the result of a BrAC measurement to thedriver. The HMI may be a multi-purpose interface, such that requestingand displaying information related to a breath test is only one of manyfunctions. Other functions may be navigation, HVAC interaction, stereosystem interaction, or other system interactions typical for a vehicle.The HMI may be integrated into the vehicle within view of the driver.

The CPU 415 is also in communication with auxiliary sensors 414, whichmay be, for example, temperature, barometric pressure or opticalsensors, or a camera to determine the testing conditions within avehicle. The auxiliary sensors 414 are used during the test 104 ofprocess 100. A data communication unit 416 may store parameter valuesused by the CPU to determine BrAC measurements and normal testingconditions of the vehicle. The data communication unit 416 alsotransfers data between the sensor system 400 and other units outside ofthe sensor 400 (not shown). The sensor 400 also includes a power unit117 for power management and supply.

FIG. 5 is an overhead view of a driver's head position in relation to asensor, according to an illustrative implementation. Auxiliary sensorsmeasure a lateral distance 510 between the driver 504 and the sensor506. The lateral distance 510 may be measured between the midline of thesensor 508 and the midline of the driver's head 504. Under normaltesting conditions, the lateral distance 510 is less than or equal to 20cm. The measurement of lateral distance 510 may occur at the test 104 ofprocess 100 as shown in FIG. 1. The determination at logic gate 108 ifthe testing conditions of the vehicle are normal takes into account thelateral distance 510 as shown in FIG. 5A. Measurement of the lateraldistance 510 may ensure that the driver is breathing directly towardsthe sensor 506 during an active breath test. Measurement of lateraldistance 510 may also ensure that during passive breath testing, thedriver is not attempting to avoid breath detection of the sensor byholding his or her head away from the direction of the sensor.

Auxiliary sensors also measure a driver's head rotation in relation tothe midline 518 of sensor 516. The rotational angle 520 may be measuredbetween the midline 518 of the sensor 516 and the midline 514 of thedriver's head 512. Under normal testing conditions, the rotational angle520 may be ±5°. The measurement of the rotational angle 520 may occur atthe test 104 of process 100 as shown in FIG. 1. The determination atlogic gate 108 of whether or not testing conditions of the vehicle arenormal takes into account the rotational angle 520 as shown in FIG. 5B.Measurement of the rotational angle 520 may ensure that the driver isbreathing directly towards the sensor 516 during an active breath test.Measurement of the rotational angle 520 may also ensure that duringpassive breath testing, the driver is not attempting to avoid breathdetection of the sensor by holding his or her head away from thedirection of the sensor.

The lateral distance 510 and rotational angle 520 may be measured by anembedded camera sensor (not shown), which may be incorporated into avehicle and placed near a driver's head. The embedded camera may alsodetermine if there is an unfamiliar object within the camera's field ofview, and/or whether a passenger is within field of view of a driver'shead.

FIG. 6 is a graph representing examples of signals detected by aninitiation sensor and BrAC sensor, according to an illustrativeimplementation. The graphs shown at 600 occur along the same time scale.Graph 602 (denoted “P”) shows a signal 604 representing the detection ofthe presence of a driver as he or she enters or prepares to enter avehicle. Signal 604 initiates the start 102 as shown in process 100 inFIG. 1. Signal 604 begins a timer that will determine the time intervalbetween the initiation signal at 604 and the detection of a breath,which is shown at graph 606 (denoted “T”). Breath is detected from apeak 608 in the concentration of a tracer gas signal. When the tracergas is CO₂, a peak in breath detection is characterized by a magnitudeof CO₂ detection at or above 525 ppm, assuming a dilution factor of 80,and assuming an end-tidal CO₂ concentration of 4.2% volume. The durationof the peak 614 is expected to be 1-3 seconds, excluding the responsetime of the sensor. The rise time of the peak 612 as well as the declinetime 616 may also be used to characterize the tracer gas signal as theresult of exhaled breath of a driver. Typical rise times may be in therange 0.5 to 1.0 seconds, while typical decline times may be in therange 3 to 5 seconds. The peak in the tracer gas signal at 610 may endthe timer. The time interval 622 may be measured and used to determineif an acceptable time limit has been exceeded between the initiationsignal 604 and the breath signal 608, such as at logic gate 110 as shownin FIG. 1.

Graph 618 shows the detection signal for EtOH. Depending on theconcentration of EtOH within a driver's breath, graph 618 may or may notshow a peak 620 corresponding to the peak 608 in the tracer gas. If,however, there is EtOH in the driver's breath, the EtOH signal 620 willbe approximately simultaneous to the tracer gas signal 608, as shown inFIG. 6. The magnitude of the peak will indicate the concentration ofBrAC in the measured breath sample. Measurement of BrAC from peak 620may occur approximately simultaneously to the detection of peak 608.

It will be understood that the foregoing is only illustrative of theprinciples of the invention, and that the invention can be practiced byother than the described embodiments, which are presented for purposesof illustration and not of limitation, and the present invention islimited only by the claims which follow.

1. A method for passive breath alcohol detection for vehicle operation,the method comprising: initiating a sensor system; passively obtaining afirst air sample; measuring a concentration of a tracer gas in the firstair sample; determining, using the sensor system, a set of testingconditions based in part on the first air sample; if the set of testingconditions is within a normal range and a peak in tracer gasconcentration is detected, measuring a Breath Alcohol Concentration(BrAC) of a driver from the first air sample; if the set of testingconditions is outside of the normal range or no peak in tracer gasconcentration is detected, requesting and actively obtaining a secondair sample from the driver and measuring the BrAC of the driver.
 2. Themethod of claim 1, further comprising: measuring a time interval betweeninitiating the sensor system and detecting the peak in tracer gasconcentration; and if the time interval exceeds a predetermined timelimit, determining that the set of testing conditions is outside of thenormal range.
 3. The method of claim 2, wherein detecting the set oftesting conditions further comprises: measuring the environmentalconditions of a vehicle.
 4. The method of claim 3, wherein measuring theenvironmental conditions of the vehicle further comprises: measuring atemperature within the vehicle; and if the temperature is outside anormal temperature range, determining that the set of testing conditionsis outside of the normal range.
 5. The method of claim 4, whereindetecting the environmental conditions of the vehicle further comprises:measuring a pressure within the vehicle; and if the pressure is outsidea normal pressure range, determining that the set of testing conditionsis outside of the normal range.
 6. The method of claim 5, whereindetecting the set of testing conditions further comprises: measuring thedriver's head position relative to a BrAC
 7. The method of claim 6,wherein initiating the sensor system further comprises: detecting thepresence of the driver entering the vehicle.
 8. The method of claim 7,wherein requesting and actively obtaining a second air sample from thedriver and measuring the BrAC of the driver further comprises:determining if a measured BrAC is at an intermediate level; and if themeasured BrAC is at an intermediate level, requesting an active thirdbreath sample and measuring BrAC.
 9. The method of claim 8, whereinactively obtaining a second air sample from the driver furthercomprises: requesting, through a human-machine interface, an undilutedbreath sample directed towards the BrAC sensor.
 10. The method of claim9, further comprising: sending a result of the driver's BrAC measurementto a central processing unit (CPU), wherein the CPU is in communicationwith the vehicle.
 11. The method of claim 10, further comprising:disabling the operation of the vehicle if the result of the driver'sBrAC measurement is above a high set point.
 12. The method of claim 11,further comprising: enabling the operation of the vehicle if the resultof the driver's BrAC is below a low set point.
 13. The method of claim10, further comprising: requesting and actively obtaining a second airsample from the driver and measuring the BrAC of the driver if a BrACresult from the first air sample is at the intermediate level.
 14. Themethod of claim 12, further comprising: continuously measuring airsamples after initiating the sensor system; and continuously measuringthe concentration of the tracer gas after the first air sample ismeasured.
 15. An apparatus for passive breath alcohol detection forvehicle operation, the apparatus comprising: sensors configured tomeasure a concentration of a tracer gas in a passively obtained firstair sample; and a processor configured to: determine, a set of testingconditions based in part on the first air sample; if the set of testingconditions is within a normal range and a peak in tracer gasconcentration is detected, measure a Breath Alcohol Concentration (BrAC)of a driver from the first air sample; if the set of testing conditionsis outside of the normal range or no peak in tracer gas concentration isdetected, request and actively obtain a second air sample from thedriver and measure the BrAC of the driver.
 16. The apparatus of claim15, further comprising: a timer configured to: measure a time intervalbetween initiating the sensors and detecting the peak in tracer gasconcentration, and wherein the processor determines that the set oftesting conditions is outside of the normal range if the time intervalexceeds a predetermined time limit.
 17. The apparatus of claim 16,wherein the sensors are further configured to: measure the environmentalconditions of a vehicle.
 18. The apparatus of claim 17, furthercomprising: a temperature sensor configured to: measure a temperaturewithin the vehicle, and wherein the processor determines that the set oftesting conditions is outside of the normal range if the temperature isoutside a normal temperature range.
 19. The apparatus of claim 18,further comprising: a pressure sensor configured to: measure a pressurewithin the vehicle, and wherein the processor determines that the set oftesting conditions is outside of the normal range if the pressure withinthe vehicle is outside a normal pressure range.
 20. The apparatus ofclaim 19, further comprising: a camera configured to measure thedriver's head position relative to a BrAC sensor. 21.-28. (canceled)